This invention pertains generally to the art of industrial vacuum loaders or cleaners. Such machines have become increasingly important in recent years because they allow their users to increase efficiency of their operations by conserving valuable materials, by reducing labor costs and by simultaneously providing cleaner and safer work environments. Such machines are commonly employed in foundries, mines, grain storage vessels, primary metal plants, minerals processing plants, municipal streets and other areas where loose materials should desirably be collected, either to recover their economic value or for puposes of cleanliness and safety. The increased interest in machines of this type has been accompanied by a corresponding development of the technology involved in their construction. Early machines, typified by leaf pick-up vehicles, employed a fan through which debris passed during collection. Later models employed exhaust type vacuum fans to suck debris through an intake hose and deposit it in a collection hopper without debris passing through the fan. Screens are sometimes employed to protect the fans, and some machines sprayed water into the air stream to remove entrained particles. Still more advanced models have employed multistage centrifugal blowers in place of single stage fans.
One known system for loading and cleaning, using such a centrifugal pump, utilizes a flexible vacuum intake hose for conveying refuse or other material into a main collection hopper. In such a system, the vacuum blower or exhauster is separated from the main hopper by a filtration means for protecting the vacuum blower from fine dust particles which may become entrained in the air stream flowing through the system. One known means for filtering dust particles utilizes filter bags for collecting the dust and reverse air flushing for periodically cleaning the filter bags. The basic principles of this type of filter are disclosed in U.S. Pat. No. Re. 24,954 for an "Apparatus for Filtering Solids from Gas-Solid Suspensions" issued May 28, 1961. Another filtration system utilizes a fabric filter media stretched over a plurality of parallel bars to form a continuous series of bags. A representative system of this type is described in U.S. Pat. No. 3,186,021 for "Power Sweeper," issued June 1, 1965 to Krier et al. The Krier et al. "bags" are cleaned by shaking the parallel bars to remove accumulated dust. Yet another filtering arrangement provides open bottomed bags which are pulsed with blasts of compressed air to expand the bags and flake off dust accumulations.
The filtering devices discussed above may be used in a variety of industrial operations such as vacuum cleaning of debris from factories or foundries, street cleaning, loading or conveying of wheat and other grains, leaf pick-up, etc. One problem which is frequently encountered with the prior vacuum cleaners and loaders is that the fan is damaged if the filtration system fails thereby allowing large amounts of dust to pass into the fan. This problem is compounded if positive displacement pumps are used in place of vacuum pumps. Positive displacement pumps are advantageously employed in large vacuum machines because they possess increased efficiency over centrifugal fans and fuel consumption for positive displacement pumps is as much as 50 percent of that required by centrifugal pumps. In addition, velocity and vacuum control can be more precise using positive displacement pumps. The difficulty up until now, however, has been that positive displacement pumps are much more susceptible to damage if filter bags fail and large amounts of dust are allowed to enter the pump.
Another problem with prior devices arises when a single machine is used to collect or load both solids and liquids. During the collection of liquid materials, the filtering media usually becomes damp, and upon switching the unit for collection of solid materials, airborne dust can form a cement-like cake on the filter. The cake cannot be removed by the normal cleaning procedure. One proposed solution to this latter problem has been to bypass the filtering media when liquids are collected. This may be accomplished by providing a manually operating switching device, and the machine operator makes whatever adjustments are necessary depending on the current use of the machine. Any error in judgement on the part of the operator could quickly result in vacuum pump damage. Because of the relatively high expense involved in the purchase of large vacuum loaders and cleaners of this type, downtime occasioned by the need to replace the filtering media or to repair or replace the vacuum pump can be costly.
A still further problem with the prior art filtration units is that they are relatively inflexible and are usually designed for a specific machine, i.e., one mounted on a truck chassis or one designed for stationary units. Those who may need filters for several types of vacuum units would then need to purchase several different filtration units, whereas such would not be the case if the filtering system were adapted to be readily connected to different vacuum cleaners and loaders.